Wildlife and domestic livestock, like these zebras and cattle near Kenya’s Maasai Mara Reserve, cohabit rangeland ecosystems throughout many parts of Africa.

And buffalo, zebras and antelopes eat grass that could feed cattle.

In the East African savannas, the interactions between wildlife and the people whose livelihood depends on cows and goats, are complicated, critical and contentious.

Grazing is about the only way to make a living in this hot, dry land, but livestock and many wild herbivores eat similar vegetation.

And so the competition is obvious: How can a cow eat forage that a zebra ate first?

The question answers itself, and so nobody studied the issue.

Not so obvious after all

But in other realms, ecologists have found that organisms that seem to compete may actually aid each other. “We are just beginning to understand that the relationship between species is highly contextual,” says Truman Young, a professor of plant sciences at the University of California at Davis, “and this interaction includes competition and facilitation. Once, people thought if two species were similar, they always competed, but years ago, it became clear that facilitation exists in certain situations.”

Young is senior author of new study showing that in Kenya’s highland savannas, competition is partly offset by facilitation; although during the dry season wildlife steal food from the mouths of cattle, so to speak, the situation is reversed during the wet season.

During the rainy season, cattle and zebra shared a lush pasture that sprouted after burning.

Well done

The study was performed during 2007 and 2008, on nine fenced plots, or “exclosures,” each 4 hectares in size. The researchers placed four young, unbred females of an African breed called Boran on each plot for 16-week periods, and measured their eating habits and weight gain in three conditions:

Cattle plus all herbivores, including the jumbo-sized elephants and giraffes

First author Wilfred Odadi, a postdoctoral researcher at Princeton University and the African Wildlife Foundation, wrote us to explain that facilitation nearly equaled competition. “Wildlife-driven depression of cattle weight gain in the dry season is 35 to 40 percent. In the wet season, cattle put on weight faster by about the same percentage when they forage with wildlife.” The real-world situation, he added, would “depend on the lengths and frequencies of dry and wet seasons.”

This was the first experimental evidence that wildlife and livestock are engaged in facilitation and competition, Young says. “There is a basic-science excitement here. With this large-vertebrate system, we have shown that you can actually sometimes have competition and sometimes facilitation.”

It’s possible that the 15-year history of experiments on the site has changed the vegetation enough to weaken the results. But the continuous grazing of cattle kept the site’s vegetation similar to the surrounding savanna, Young says. “If we had excluded all large herbivores, the rangeland would become very different, and our inferences would be skewed. But because cattle are the dominant herbivores … the plots were not that different. My belief is if we had started the exclosures last year, we would have gotten the same result.”

In Eastern Serengeti, Tanzania, a Maasai herdsman tends his goats with a Thompson’s gazelle in the background. Maasai herders were hired to tend cattle in the Odadi experiment.

What are the practical implications?

Killing wildlife, except for rogue animals, is illegal in Kenya, but it still happens, Odadi told us. “Because in Kenya wildlife belongs to the state, and not to the land owner, some livestock keepers still show a negative attitude towards wildlife because of perceived ‘detrimental’ effects on livestock including competition, livestock depredation and disease transmission. Some people react by fencing off their properties to keep wildlife away. There are also situations where water sources are fenced off by pastoralists to make them inaccessible to wildlife. In extreme cases, wild animals are actually killed, albeit illegally.”

Africa’s seasonally dry, grassland savannas cover a large portion of the continent.

And so in a region with unreliable rainfall and few resources, it’s good news for advocates of biodiversity conservation that the competition between domestic and wild ungulates, at least on savannas, may be more apparent than real.

Good news for conservation

Indeed, large mammal ecologist Johan du Toit of Utah State University, wrote in Science that the new information should eventually “provide managers with opportunities to capitalize on facilitative interactions, intervene against competitive ones, and enhance animal production overall.”

Rangeland managers often mix native and non-native plants, du Toit added. And after “bold experimentation and a break from orthodoxy,” a similar approach with animals could boost production while conserving biodiversity.

Odadi says better knowledge of cattle-wildlife interactions could support short-term changes, such as slaughtering or marketing livestock “at the end of the wet season, when they have recovered from competition in the preceding dry season, and also to minimize competitive effects (by reducing densities) in the next dry season.”

Conservationists in East Africa and elsewhere are seeking “to manage land for ecosystem biodiversity and short-term extractive value,” says Young, “but it’s pretty hard to find good examples, other than assertions about the profitability of ecotourism. We were able to show that wildlife and cattle have a complex interaction; that wildlife is not uniformly bad for cattle, and that allows us to be a little more lenient toward wildlife.”